Heat the oven to 170C/fan 150C/gas 31/2. Butter a 900g loaf tin and line the base and ends with a strip of baking paper. Put the butter, sugar, Aperol, almond extract, orange zest and juice into a large bowl with the whole egg and one yolk. Beat with an electric whisk for a few minutes until really pale and fluffy. Fold in the flour and ground almonds.
Clean the whisk and, in a clean mixing bowl, whisk the remaining three egg whites to stiff peaks.
Stir 1/3 of the egg whites into the batter to loosen it, then gently fold in the rest with a big metal spoon or spatula, keeping in as much air as possible. Spoon into the loaf tin and gently level the top. Bake on a middle shelf for 1 hour 10 minutes, until risen and a skewer poked into the centre comes out clean. If it’s not cooked through, return to the oven for 10-minute increments before checking again.
As soon as the cake comes out of the oven, use a skewer to poke holes all over the top of the hot cake, then gradually spoon 2 tbsp of Aperol over the top. Mix the remaining Aperol with the lemon juice, then pour in the granulated sugar. Quickly stir to dissolve all the sugar, then immediately spoon over the cake to cover it completely. Leave in the tin until the cake is cool and the topping has set to a sugary crust.